The Collaborative International Dictionary of English v.0.48:

mountaineering \moun`tain*eer"ing\ (moun`t[i^]n*[=e]r"[i^]ng),
   n.
   Climbing mountains as a sport.
   [PJC]

WordNet (r) 3.0 (2006):

mountaineering
    n 1: the activity of climbing a mountain [syn: mountain
         climbing, mountaineering]